During the next 90 minutes, 17 other hijackers stroll through security and board their flights, armed with knives or box cutters that none of the screening methods detect.

American Airlines Flight 11 takes off slightly late at 7:59 am, just as a conference opens in the Windows on the World bar at the top of the World Trade Center in New York.

Then in the next 20 minutes, United Airlines Flight 175 takes off, followed by American Airlines Flight 77 from Washington Dulles International Airport bound for Los Angeles. At 8:42 am, United Airlines Flight 93 departs Newark, following a lengthy delay.

As fire and smoke belch from the building, people in the second of the Twin Towers are instructed to stay put. Then at 9:02 am that advice is reversed and a public announcement says: "You may wish to start an orderly evacuation."

Police and firefighter crews are already racing en masse to the bottom of Manhattan, little knowing how bad things will get.

One minute later, at 9:03 am, Flight 175 crashes into floors 77 to 85 of the South Tower.

President George W. Bush, visiting a Florida elementary school, has already been told about the first crash, which many assumed was an accident.

The president has sat down to read children "The Pet Goat" when the second plane hits. At 9:05 am, Bush's chief of staff Andrew Card bends over and whispers in his right ear: "America is under attack."

As thousands of first responders rush into the burning towers, and thousands of office workers stream out, vice president Dick Cheney is evacuated from his normal White House office into a bunker.

A minute later, at 9:37 am, Flight 77 smashes into the Pentagon's west facade. "At first I thought I've blown up the fax machine. Then I realized it wasn't me. I smell the jet fuel," an accountant in the building recalls for the 9/11 memorial in New York.

Over the next hours, a vast search and rescue effort begins in the apocalyptic scene in lower Manhattan. Amazingly, 14 people are found alive inside the rubble of the North Tower, where part of the stairwell shielded them from the collapse.